Forensic entomology—the study of insects and other arthropods in relation to legal investigations, especially in relation to the decomposition of cadavers—is limited in determining whether a corpse has been relocated, according to a new report published in open-access journal PeerJ. The report, which compiles and analyzes data from over 170 publications, found that the presence of certain insects should only be used to determine body relocation on a case-by-case basis, and relying on specific local data and experiments as opposed to general trends. The report is authored by Damien Charabidze of Lille University with co-authors Matthias Gosselin and Valéry Hedouin.

Spatial separation of species, behavior and developmental stages of insects, phenology and colonization time, and molecular analysis were the four main areas explored in the report in relation to determining whether a body had been moved from one place to another prior to discovery. Each approach had its limitations. In its analysis of dozens of studies, experiments and case examples, the report found that results often varied from case to case, and that outlying cases—such as one in which fresh fly egg batches were found in a dark cave, when fly eggs are typically only laid during daylight—meant relocation could not be determined with absolute certainty based on the presence of a specific species or life stage.

The discovery of certain species on a corpse in a certain geographic location was found to be of limited value due to the large distribution of the insect species most commonly found on cadavers, although the report focused mostly on the distribution of species across Europe. For example, one species, Chrysomya albiceps was noted as being a potential indicator of corpse relocation if found outside of southern Europe, where the species is mostly found. However, Chrysomya albiceps has also been found to migrate to the north during hot summer months, meaning relocation cannot be determined with certainty based on its presence.

The report also found limited value in the use of forensic entomology to determine relocation to and from indoor and outdoor environments, open and forested areas, sunny and shady spots, and urban and rural regions. Each situation involved observed outliers that would decrease the certainty to which one could say a body was relocated from one environment to another. However, the report found that relocation could be more easily determined if it occurred between water and land, due to the presence of aquatic invertebrates that would indicate the presence of water, and land species that would be unlikely to lay their eggs on a cadaver that is submerged or floating in water. However, the authors still warn against the use of generalized trends to draw conclusions, as some land species have been observed laying eggs on exposed parts of floating cadavers and carcasses.

Investigators could potentially determine if a corpse has been previously buried from the presence of species—such as Phylloteles pictipennis and Eumacronychia persolla—that depend on buried food resources, but other species commonly found on buried bodies—such as Conicera tibialis and Megaselia scalaris—have also been observed in open environments and indoors, which is more cause for caution in drawing conclusions. The report notes that the presence of corpse-eating species in an indoor location could determine that a body was previously present, but other factors, such as the previous presence of garbage or a nearby cadaver from which the insects migrated after feeding should be considered. The presence of crushed or flattened insects and pupae underneath a cadaver were considered another potential sign of relocation.

Molecular analysis of cuticular hydrocarbons—a thin layer of wax consisting of free lipids produced on the surface of insects’ bodies—could be helpful in determining relocation due to geographical differences in the composition of this substance on specimens from the same species. The report suggests more research into this possibility, as well as the expansion of databases of insect DNA that could determine genetic differences between separate populations of the same species. The presence of human DNA in the guts of corpse-eating insects was noted as a possible identifier of a victim whose body has not been located, and the authors point out at least one reported case of this being done. However, insects’ digestive enzymes quickly degrade DNA, leaving a short period of time—about two days, according to the report—for this information to be collected.

The report concludes that local data and experiments should be referenced to determine corpse relocation from insect evidence, and states, “Corpse relocation inferences should not be based on general trends or previous results at a broader scale.” However, it adds that increased sharing of forensic entomology databases should be a future focus in this area to increase the availability of scientific information to the forensic community.